This invention generally relates to polymeric fibers and filaments and products such as nonwoven fabrics made with polymeric fibers and filaments. More particularly, this invention relates to single component and multicomponent polymeric fibers and filaments which include propylene polymer compositions, and nonwoven fabrics and garments made with such fibers and filaments.
Polymeric fibers and filaments are used to make a variety of products including yarns, carpets, woven fabrics, and nonwoven fabrics. As used herein, polymeric fibers and filaments are referred to generically as polymeric strands. Filaments mean continuous strands of material and fibers mean cut or discontinuous strands having a definite length.
It is often desirable that polymeric strands and articles made with polymeric strands be soft and strong. This is particularly true for nonwoven fabric and articles made with nonwoven fabric. Nonwoven fabrics are typically used to make garments such as work wear, medical apparel, and absorbent articles. Absorbent products made with nonwoven fabric include infant care items such as diapers, child care items such as training pants, feminine care items such as sanitary napkins, and adult care items such as incontinence products.
Nonwoven fabrics are commonly made by meltspinning thermoplastic materials. Meltspun fabrics are called spunbond materials and methods for making spunbond materials are well-known. U.S. Pat. No. 4,692,618 to Dorschner et al. and U.S. Pat. No. 4,340,563 to Appel et al. both disclose methods for making spunbond nonwoven webs from thermoplastic materials by extruding the thermoplastic material through a spinneret and drawing the extruded material into filaments with a stream of high velocity air to form a random web on a collecting surface. For example, U.S. Pat. No. 3,692,618 to Dorschner et al. discloses a process wherein bundles of polymeric filaments are drawn with a plurality of eductive guns by very high speed air. U.S. Pat. No. 4,340,563 to Appel et al. discloses a process wherein thermoplastic filaments are drawn through a single wide nozzle by a stream of high velocity air. The following patents also disclose typical meltspinning processes: U.S. Pat. No. 3,338,992 to Kinney; U.S. Pat. No. 3,341,394 to Kinney; U.S. Pat. No. 3,502,538 to Levy; U.S. Pat. No. 3,502,763 to Hartmann, U.S. Pat. No. 3,909,009 to Hartmann; U.S. Pat. No. 3,542,615 to Dobo et al.; and Canadian Patent Number 803,714 to Harmon.
Spunbond materials with desirable combinations of physical properties, especially combinations of strength, durability, and softness have been produced, but limitations have been encountered. For example, in some applications, polymeric materials such as polypropylene may have a desirable level of strength but not a desirable level of softness. On the other hand, materials such as polyethylene may, in some cases, have a desirable level of softness but a not a desirable level of strength.
In an effort to produce nonwoven materials having desirable combinations of physical properties, nonwoven fabrics comprising multicomponent strands such as bicomponent strands or multiconstituent strands such as biconstituent strands have been developed.
Methods for making bicomponent nonwoven materials are well-known and are disclosed in patents such as U.S. Pat. No. Reissue 30,955 of U.S. Pat. No. 4,068,036 to Stanistreet, U.S. Pat. No. 3,423,266 to Davies et al., and U.S. Pat. No. 3,595,731 to Davies et al. A bicomponent nonwoven fabric is made from polymeric fibers or filaments including first and second polymeric components which remain distinct. The first and second components of multicomponent strands are arranged in substantially distinct zones across the cross-section of the strands and extend continuously along the length of the strands. Typically, one component exhibits different properties than the other so that the strands exhibit properties of the two components. For example, one component may be polypropylene which is relatively strong and the other component may be polyethylene which is relatively soft. The end result is a strong yet soft nonwoven fabric.
Multiconstituent strands are similar to multicomponent strands except that one component does not extend continuously along the length of the strands. The noncontinuous component is typically present as a multitude of discrete polymer segments connected by the other polymeric component.
Although conventional bicomponent and biconstituent nonwoven fabrics have desirable levels of strength, durability, and softness, there is still a need for nonwoven materials which are made with polymeric strands and have particular combinations of strength, durability, and softness. Furthermore, there is a need for garments made with nonwoven materials having particular combinations of strength, durability, and softness.
Accordingly, an object of the present invention is to provide improved polymeric strands and products made therewith such as nonwovens and garments.
Another object of the present invention is to provide polymeric strands, nonwoven fabrics made with polymeric strands, and articles such as garments made with nonwoven fabrics, each having desirable levels of strength, durability, and softness.
A further object of the present invention is to provide soft yet strong and durable garments such as medical apparel, workwear, and absorbent articles.
Thus, the present invention provides a polymeric strand including a first polymeric component comprising a blend of:
(a) a melt-extrudable polyolefin; and
(b) a polypropylene composition comprising:
(i) a first polymer which is a propylene polymer comprising 85% by weight of propylene and having an isotactic index greater than 85;
(ii) a second polymer which is a polymer comprising ethylene and being insoluble in xylene at about 23xc2x0 C.; and
(iii) a third polymer which is an amorphous copolymer of ethylene and propylene, the amorphous copolymer being soluble in xylene at about 23xc2x0 C.
The polypropylene composition is preferably present in the first polymeric component in an amount up to about 40% by weight. In addition, the first polymer is preferably present in the polypropylene composition in an amount from about 10 to about 60 parts by weight, the second polymer is preferably present in the polypropylene composition in an amount from about 10 to about 40 parts by weight, and the third polymer is preferably present in the polypropylene composition in an amount from about 30 to about 60 parts by weight. Still more particularly, the third polymer preferably includes ethylene in an amount from about 40 to about 70% by weight. The polypropylene composition, by itself, is heterophasic and normally not melt-spinable into strands, and particularly not into spunbond strands.
Suitable melt-extrudable polyolefins for the first polymeric component include crystalline polyolefins, and more particularly, include polypropylene, random copolymers of propylene and ethylene, and poly(4-methyl-1-pentene).
According to another aspect of the present invention, the polymeric strand is a multicomponent strand and further includes a second melt-extrudable polymeric component. The first and second components of the multicomponent strand are arranged in substantially distinct zones across the cross-section of the multicomponent strand and extend continuously along the length of the multicomponent strand. The first component of the multicomponent strand constitutes at least a portion of the peripheral surface of the strand continuously along the length of the strand.
More particularly, the second component of the multicomponent strand includes a crystalline polyolefin. Suitable polyolefins for the second component of the multicomponent strand include polypropylene, random copolymers of propylene and ethylene and poly(4-methyl-1-pentene). Suitable configurations for the first and second components of the multicomponent strand include a side-by-side configuration and a sheath/core configuration.
The present invention also comprehends a nonwoven fabric made with the above described polymeric strands and further comprehends garment materials made with such nonwoven fabric. The addition of the heterophasic polypropylene composition enhances the strength of the polymeric strands and the nonwoven fabric and garments made therewith while maintaining, and sometimes enhancing, acceptable levels of durability and softness.
Still further objects and the broad scope of the applicability of the present invention will become apparent to those of skill in the art from the details given hereafter. However, it should be understood that the detailed description of the preferred embodiments of the present invention is only given by way of illustration because various changes and modifications well within the spirit and scope of the invention should become apparent to those of skill in the art in view of the following detailed description.